Peculiarities of macrozoobenthos in the offshore zone of a small artificial post-gravel pit reservoir

The offshore macrozoobenthos and selected environmental parameters were studied in a small artificial reservoir, created through sand and gravel extraction. The results are rather surprising. Despite the shallow depth and good wind exposure of the reservoir, a thermal and oxygen stratification developed in the summer, causing hypoxic conditions near the bottom, even though the organic matter content in the sediments was <5%. Furthermore, despite the high fish abundance, chaoborids prevailed in zoobenthos, while Tanytarsus sp. and Chironomus sp. co-dominated among chironomids. This study attempts to explain the observed phenomena, though the presented hypotheses still need further confirmation.